Thermal control apparatus for inductively coupled RF plasma reactor having an overhead solenoidal antenna

ABSTRACT

The invention is embodied in a plasma reactor including a plasma reactor chamber and a workpiece support for holding a workpiece near a support plane inside the chamber during processing, the chamber having a reactor enclosure portion facing the support, a cold body overlying the reactor enclosure portion, a plasma source power applicator between the reactor enclosure portion and the cold body and a thermally conductor between and in contact with the cold body and the reactor enclosure. The thermal conductor and the cold sink define a cold sink interface therebetween, the reactor preferably further including a thermally conductive substance within the cold sink interface for reducing the thermal resistance across the cold sink interface. The thermally conductive substance can be a thermally conductive gas filling the cold body interface. Alternatively, the thermally conductive substance can be a thermally conductive solid material. The reactor can include a gas manifold in the cold body communicable with a source of the thermally conductive gas an inlet through the cold body from the gas manifold and opening out to the cold body interface. The reactor can further include an O-ring apparatus sandwiched between the cold body and the thermal conductor and defining a gas-containing volume in the cold body interface of nearly infinitesimal thickness in communication with the inlet from the cold body. More generally, the reactor can include the facilitation of thermal transfer across an interface between a hot and/or cold sink and any part exposed to the reactor chamber interior atmosphere, such as the ceiling, wall or polymer-hardening precursor ring, for example, by the insertion into that interface of a thermally conductive gas or substance.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/648,254 Filed May 13, 1996 pending by Kenneth S. Collins etal entitled "INDUCTIVELY COUPLED RF PLASMA REACTOR HAVING AN OVERHEADSOLENOIDAL ANTENNA", which is a continuation-in-part of Ser. No.08/580,026 filed Dec. 20, 1995 pending by Kenneth S. Collins et al.which is a continuation of Ser. No. 08/041,796 filed Apr. 1, 1993, nowU.S. Pat. No. 5,556,501 which is a continuation of Ser. No. 07/722,340filed Jun. 27, 1991 now abandoned; and a continuation-in-part of Ser.No. 08/503,467 filed Jul. 18, 1995 by Michael Rice et al. now U.S. Pat.No. 5,770,099 which is a divisional of Ser. No. 08/138,060 filed Oct.15, 1993 now U.S. Pat. No. 5,477,975; and continuation-in-part of Ser.No. 08/597,577 filed Feb. 2, 1996 allowed by Kenneth Collins, which is acontinuation-in-part of Ser. No. 08/521,668 filed Aug. 31, 1995 (nowabandoned), which is a continuation-in-part of Ser. No. 08/289,336 filedAug. 11, 1994 now abandoned, which is a continuation of Ser. No.07/984,045 filed Dec. 1, 1992 (now abandoned). In addition U.S.application Ser. No. 08/648,256 filed May 13, 1996 allowed by Kenneth S.Collins et al. entitled "Plasma With Heated Source of aPolymer-Hardening Precursor Material" discloses related subject matter.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention is related to heating and cooling apparatus in aninductively coupled RF plasma reactors of the type having a reactorchamber ceiling overlying a workpiece being processed and an inductivecoil antenna adjacent the ceiling.

2. Background Art

In a plasma processing chamber, and especially in a high density plasmaprocessing chamber, RF (radio frequency) power is used to generate andmaintain a plasma within the processing chamber. As disclosed in detailin the above-referenced applications, it is often necessary to controltemperatures of surfaces within the process chamber, independent of timevarying heat loads imposed by processing conditions, or of other timevarying boundary conditions. In some cases where the window/electrode isa semiconducting material, it may be necessary to control thetemperature of the window/electrode within a temperature range to obtainthe proper electrical properties of the window. Namely, for thewindow/electrode to function simultaneously as a window and as anelectrode, the electrical resistivity is a function of temperature forsemiconductors, and the temperature of the window/electrode is bestoperated within a range of temperatures. The application of RF power togenerate and maintain the plasma leads to heating of surfaces within thechamber, including windows (such as used for inductive orelectromagnetic coupling of RF or microwave power) or electrodes (suchas used for capacitive or electrostatic coupling of RF power, or forterminating or providing a ground or return path for such capacitive orelectrostatic coupling of RF power) or for combinationwindow/electrodes. Heating of those surfaces can occur due to 1) ion orelectron bombardment, 2) absorption of light emitted from excitedspecies, 3) absorption of power directly from the electromagnetic orelectrostatic field, 4) radiation from other surfaces within thechamber, 5) conduction (typically small effect at low neutral gaspressure), 6) convection (typically small effect at low mass flowrates), 7) chemical reaction (i.e. at the surface of the window orelectrode due to reaction with active species in plasma).

Depending on the process being performed with the plasma processchamber, it may be necessary to heat the window or electrode to atemperature above that temperature which the window or electrode wouldreach due to internal sources of heat as described above, or it may benecessary to cool the window or electrode to a temperature below thattemperature which the window or electrode would reach due to internalsources of heat during some other portion of the operating process orsequence of processes. In such cases, a method for coupling heat intothe window or electrode and a method for coupling heat out of the windowor electrode is required.

Approaches for heating window/electrodes from outside the processchamber include the following:

1. heating the window/electrode by an external source of radiation(i.e., a lamp or radiant heater, or an inductive heat source),

2. heating the window/electrode by an external source of convection(i.e. forced fluid, heated by radiation, conduction, or convection),

3. heating the window/electrode by an external source of conduction(i.e., a resistive heater).

The foregoing heating methods, without any means for cooling, limit thetemperature range available for window or electrode operation totemperatures greater than the temperature which the window or electrodewould reach due to internal sources of heat alone.

Approaches for cooling window/electrodes from outside the processchamber include the following:

1. cooling the window/electrode by radiation to a colder externalsurface,

2. cooling the window/electrode by an external source of convection(i.e., natural or forced),

3. cooling the window/electrode by conduction to an external heat sink.

The foregoing cooling methods, without any means for heating other thaninternal heat sources, limit the temperature range available for windowor electrode operation to temperatures less than that temperature whichthe window or electrode would reach due to internal sources of heatalone.

Additionally the foregoing cooling methods have the following problems:

1. cooling the window/electrode by radiation is limited to low heattransfer rates (which in many cases are insufficient for the window orelectrode temperature range required and the rate of internal heating ofwindow or electrodes) at low temperatures due to the T⁴ dependence ofradiation power, where T is the absolute (Kelvin) temperature of thesurface radiating or absorbing heat;

2. cooling the window/electrode by an external source of convection canprovide large heat transfer rates by using a liquid with high thermalconductivity, and high product of density & specific heat when high flowrates are used, but liquid convection cooling has the followingproblems:

A) it is limited to maximum temperature of operation by vapor pressuredependence of liquid on temperature (i.e. boiling point) (unless a phasechange is allowed, which has its own problems--i.e. fixed temperature ofphase change--no control range, as well safety issues),

B) incompatibility of liquid cooling with the electrical environment,depending upon liquid electrical properties,

C) general integration issues with liquid in contact with reactorstructural elements. Cooling the window or electrode by an externalsource of convection (e.g., a cooling gas) is limited to low heattransfer rates which in many cases are insufficient for the window orelectrode temperature range required and the rate of internal heating ofwindow or electrodes;

3. cooling the window/electrode by conduction to an external heat sinkcan provide high rates of heat transfer if the contact resistancebetween the window or electrode and the heat sink is sufficiently low,but low contact resistance is difficult to attain in practice.

Approaches for both heating and cooling window/electrodes from outsidethe process chamber include heating the window/electrode by an externalsource of conduction (i.e., a resistive heater) in combination withcooling the window/electrode by conduction to an external heat sink. Inone implementation, the structure is as follows: a window or electrodehas a heater plate (a plate with an embedded resistive heater) adjacentan outer surface of the window electrode. Additionally, a heat sink(typically liquid cooled) is placed proximate the opposite side of theheater plate from the window or electrode. Contact resistances arepresent between window or electrode and heater plate, and between theheater plate and the heat sink. In such a system integrated withautomatic control of window or electrode temperature, a temperaturemeasurement is made (continuously or periodically) of the window orelectrode to be controlled, the temperature measurement is compared witha set point temperature, and based on the difference between themeasured and set point temperatures a controller determines through acontrol algorithm how much power to apply to the resistive heater, oralternatively, how much cooling to apply to the heat sink, and thecontroller commands output transducers to output the determined heatingor cooling levels. The process is repeated (continuously orperiodically) until some desired degree of convergence of the window orelectrode temperature to the set point temperature has occurs, and thecontrol system remains active ready to respond to changes inrequirements of heating or cooling levels due to changes in internalheat or cooling levels or to changes in the set point temperature.Besides contact resistance problems that limit the cooling capability ofthe system to control the temperature of the window or electrode, thesystem exhibits a time lag in transferring heat from the window orelectrode to the head sink as required when the internal heating orcooling load changes during plasma reactor operation. This is due inpart to the contact resistance between the window or electrode and theheater, and contact resistance between the heater and the heat sink, aswell as the thermal capacitance of the heater and the window orelectrode. For example, as the internal heat load is increased in aprocess or sequence of processes, the system senses the increase bymeasuring an increase in window or electrode temperature. As describedabove, the system reduces the heater power or increases the coolingpower in response to the increase in window or electrode temperature,but there is a lag time for the heat to diffuse through the window orelectrode, across the contact resistance between window or electrode andheater, through the heater plate, across the contact resistance betweenthe heater and heat sink. In addition, "excess" heat energy "stored" inthe heater diffuses across the contact resistance between the heater andheat sink. This lag causes more difficulty in controlling thetemperature of the window or electrode as the internal heat or coolingload changes, typically resulting in some oscillation of the window orelectrode temperature about the set point.

A further problem for a window or window/electrode (of the type thatallows electromagnetic or inductive RF or microwave power to be coupledfrom outside the chamber to inside the chamber via the window orwindow/electrode) is that the presence of heat transfer apparatus(heater and/or heat sinks) interferes with the coupling of suchelectromagnetic or inductive RF or microwave power, and/or the presenceof RF or microwave power coupling apparatus may interfere with heattransfer between heater and/or heat sink and window or window/electrode.

Thus a method is sought for heating and/or cooling a window or electrodeor window electrode used in a plasma processing chamber so that thetemperature of the window or electrode or window/electrode may becontrolled sufficiently close to a set point such that a desired processor sequence of processes may be carried out within the plasma processchamber, independent of the change of internal heating or cooling loadswithin the chamber or changes in other boundary conditions.

Additionally, a method is sought for heating and/or cooling a window orwindow/electrode used in a plasma processing chamber so that thetemperature of the window or electrode or window/electrode may becontrolled sufficiently close to a set point temperature, withoutinterference to coupling of electromagnetic or inductive RF or microwavepower through the window or window/electrode such that a desired processor sequence of processes may be carried out within the plasma processchamber, independent of the change of internal heating or cooling loadswithin the chamber or changes in other boundary conditions.

Additionally, a method is sought for heating and/or cooling an electrodeor window/electrode used in a plasma processing chamber so that thetemperature of the electrode or window/electrode may be controlledsufficiently close to a set point temperature, without interfering withcapacitive or electrostatic coupling of RF power, or interfering withterminating or providing a ground or return path for such capacitive orelectrostatic coupling of RF power, such that a desired process orsequence of processes may be carried out within the plasma processchamber, independent of the change of internal heating or cooling loadswithin the chamber or changes in other boundary conditions.

Additionally, a method is sought for heating and/or cooling a window orelectrode or window/electrode used in a plasma processing chamber sothat the temperature of the electrode or window/electrode may becontrolled sufficiently close to a set point temperature, withoutinterfering with capacitive or electrostatic coupling of RF power, orinterfering with terminating or providing a ground or return path forsuch capacitive or electrostatic coupling RF power, and withoutinterfering with coupling of electromagnetic or inductive RF ormicrowave power through the window or window/electrode such that adesired process or sequence of processes may be carried out within theplasma process chamber, independent of the change of internal heating orcooling loads within the chamber or changes in other boundaryconditions.

SUMMARY OF THE INVENTION

The invention is embodied in a plasma reactor including a plasma reactorchamber and a workpiece support for holding a workpiece near a supportplane inside the chamber during processing, the chamber having a reactorenclosure portion "facing the support, a cold sink (also referred to asa cold plate and/or cold body) overlying the reactor" enclosure portion,a plasma source power applicator between the reactor enclosure portionand the cold sink and a thermal conductor between and in contact withthe cold sink and the reactor enclosure. Preferably, the powerapplicator includes plural radially dispersed applicator elementsdefining voids therebetween and the thermal conductor includes radiallydispersed thermally conductive elements in the voids and contacting thecold sink and the reactor enclosure portion. The radially dispersedthermally conductive elements preferably include respective concentriccylindrical rings. The reactor enclosure portion includes a ceiling, theceiling including a window for power emanating from the plasma sourcepower applicator. The power applicator preferably includes an inductiveantenna in communication with an RF power generator and the ceiling isinductive power window. The ceiling preferably but not necessarilyincludes a semiconductor window electrode. The thermal conductor and thecold sink define a cold sink interface therebetween, the reactorpreferably further includes a thermally conductive substance within thecold sink interface for reducing the thermal resistance across the coldsink interface. The thermally conductive substance can be a thermallyconductive gas filling the cold sink interface. Alternatively, thethermally conductive substance can be a thermally conductive solidmaterial. The reactor can include a gas manifold in the cold sinkcommunicable with a source of the thermally conductive gas an inletthrough the cold sink from the gas manifold and opening out to the coldsink interface. The reactor can further include an O-ring apparatussandwiched between the cold sink and the thermal conductor and defininga gas-containing volume in the cold sink interface in communication withthe inlet from the cold sink. The gas-containing volume preferably is ofnearly infinitesimal thickness. The thermal conductor can be integrallyformed with the reactor enclosure portion. Alternatively, the thermalconductor can be formed separately from the reactor enclosure portionwhereby a reactor enclosure interface is defined between the reactorenclosure portion and the thermal conductor, in which case preferablythere is a thermally conductive substance within the reactor enclosureinterface for reducing the thermal resistance across the reactorenclosure interface. The thermally conductive substance in the reactorenclosure interface can be a thermally conductive gas filling thereactor enclosure interface. Alternatively, the thermally conductivesubstance in the reactor enclosure interface includes a thermallyconductive solid material. If the thermal conductor is formed separatelyfrom the reactor enclosure portion whereby a reactor enclosure interfaceis defined between the reactor enclosure portion and the thermalconductor, then preferably there is a thermally conductive gas fillingthe reactor enclosure interface for reducing the thermal resistanceacross the reactor enclosure interface. In this case, preferably thereis a gas channel through the thermal conductor and communicating betweenthe cold sink interface and the reactor enclosure interface. Preferablyin this case, there is further an O-ring apparatus between the reactorenclosure portion and the thermal conductor defining a gas-containingvolume in the reactor enclosure interface in communication with the gaschannel of the thermal conductor. Preferably, the thermally conductivesolid material includes a soft metal of the type including one ofaluminum, indium, copper, nickel. Alternatively, the thermallyconductive solid material includes an elastomer impregnated withparticles of a thermally conductive material. The particles can be of asoft metal, such as a thermally conductive material including one ofaluminum, indium, copper, nickel. Alternatively, the particles can be ofa high electrical resistivity and high thermal conductivity, such asboron nitride, high resistivity silicon carbide, high resistivitysilicon, aluminum nitride, aluminum oxide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away side view of an inductively coupled plasma reactorof the type employed in a co-pending U.S. patent application referred toabove employing generally planar coil antennas.

FIG. 2 is a log-log scale graph of induction field skin depth in aplasma in cm (solid line) and of electron-to-neutral elastic collisionmean free path length (dashed line) as functions of pressure in torr(horizontal axis).

FIG. 3A is a graph of plasma ion density as a function of radialposition relative to the workpiece center in the reactor of FIG. 1 for aworkpiece-to-ceiling height of 4 inches, the curves labelled A and Bcorresponding to plasma ion densities produced by outer and inner coilantennas respectively.

FIG. 3B is a graph of plasma ion density as a function of radialposition relative to the workpiece center in the reactor of FIG. 1 for aworkpiece-to-ceiling height of 3 inches, the curves labelled A and Bcorresponding to plasma ion densities produced by outer and inner coilantennas respectively.

FIG. 3C is a graph of plasma ion density as a function of radialposition relative to the workpiece center in the reactor of FIG. 1 for aworkpiece-to-ceiling height of 2.5 inches, the curves labelled A and Bcorresponding to plasma ion densities produced by outer and inner coilantennas respectively.

FIG. 3D is a graph of plasma ion density as a function of radialposition relative to the workpiece center in the reactor of FIG. 1 for aworkpiece-to-ceiling height of 1.25 inches, the curves labelled A and Bcorresponding to plasma ion densities produced by outer and inner coilantennas respectively.

FIG. 3E is a graph of plasma ion density as a function of radialposition relative to the workpiece center in the reactor of FIG. 1 for aworkpiece-to-ceiling height of 0.8 inches, the curves labelled A and Bcorresponding to plasma ion densities produced by outer and inner coilantennas respectively.

FIG. 4A is a cut-away side view of a plasma reactor employing a singlethree-dimensional center non-planar solenoid winding.

FIG. 4B is an enlarged view of a portion of the reactor of FIG. 4Aillustrating a preferred way of winding the solenoidal winding.

FIG. 4C is a cut-away side view of a plasma reactor corresponding toFIG. 4A but having a dome-shaped ceiling.

FIG. 4D is a cut-away side view of a plasma reactor corresponding toFIG. 4A but having a conical ceiling.

FIG. 4E is a cut-away side view of a plasma reactor corresponding toFIG. 4D but having a truncated conical ceiling.

FIG. 5 is a cut-away side view of a plasma reactor employing inner andouter vertical solenoid windings.

FIG. 6 is a cut-away side view of a plasma reactor corresponding to FIG.5 in which the outer winding is flat.

FIG. 7A is a cut-away side view of a plasma reactor corresponding toFIG. 4 in which the center solenoid winding consists of plural uprightcylindrical windings.

FIG. 7B is a detailed view of a first implementation of the embodimentof FIG. 7A.

FIG. 7C is a detailed view of a second implementation of the embodimentof FIG. 7A.

FIG. 8 is a cut-away side view of a plasma reactor corresponding to FIG.5 in which both the inner and outer windings consist of plural uprightcylindrical windings.

FIG. 9 is a cut-away side view of a plasma reactor corresponding to FIG.5 in which the inner winding consists of plural upright cylindricalwindings and the outer winding consists of a single upright cylindricalwinding.

FIG. 10 is a cut-away side view of a plasma reactor in which a singlesolenoid winding is placed at an optimum radial position for maximumplasma ion density uniformity.

FIG. 11 is a cut-away side view of a plasma reactor corresponding toFIG. 4 in which the solenoid winding is an inverted conical shape.

FIG. 12 is a cut-away side view of a plasma reactor corresponding toFIG. 4 in which the solenoid winding is an upright conical shape.

FIG. 13 is a cut-away side view of a plasma reactor in which thesolenoid winding consists of an inner upright cylindrical portion and anouter flat portion.

FIG. 14 is a cut-away side view of a plasma reactor corresponding toFIG. 10 in which the solenoid winding includes both an inverted conicalportion and a flat portion.

FIG. 15 is a cut-away side view of a plasma reactor corresponding toFIG. 12 in which the solenoid winding includes both an upright conicalportion and a flat portion.

FIG. 16 illustrates a combination of planar, conical and dome-shapedceiling elements.

FIG. 17A illustrates a separately biased silicon side wall and ceilingand employing electrical heaters.

FIG. 17B illustrates separately biased inner and outer silicon ceilingportions and employing electrical heaters.

FIG. 18 is a cut-away cross-sectional view illustrating a firstembodiment of the present invention having a thermally conductive gasinterface at each face of the thermally conductive torus of FIG. 5.

FIG. 19 is a cut-away cross-sectional view illustrating a secondembodiment of the present invention having a thermally conductive gasinterface at the one face of a thermally conductive torus integrallyformed with the semiconductor window electrode.

FIG. 20 is a cut-away cross-sectional view illustrating a thirdembodiment of the present invention having a thermally conductive solidinterface material at each face of the thermally conductive torus ofFIG. 5.

FIG. 21 is a cut-away cross-sectional view illustrating a fourthembodiment of the present invention having a thermally conductive solidinterface material at the one face of a thermally conductive torusintegrally formed with the semiconductor window electrode.

FIG. 22 is a cut-away cross-sectional view illustrating a fifthembodiment of the present invention in which the disposablesilicon-containing ring of FIG. 5 is cooled by a cold plate with athermally conductive gas interface between the cold plate and thedisposable silicon ring.

FIG. 23 is a cut-away cross-sectional view illustrating a sixthembodiment of the present invention in which the disposablesilicon-containing ring of FIG. 5 is cooled by a cold plate with athermally conductive solid interface material between the cold plate andthe disposable silicon ring.

FIG. 24 illustrates a seventh embodiment of the present invention inwhich the chamber wall and an interior chamber liner are cooled using athermally conductive gas in the interfaces across the heat conductionpaths.

FIG. 25 illustrates a modification of the embodiment of FIG. 24 in whichthe interfaces are each filled with a solid thermally conductive layerinstead of the thermally conductive gas.

FIG. 26 illustrates the embodiment of FIG. 22 in which the ring iselectrostatically clamped to seal the thermally conductive gas.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Disclosure of the Parent Application

In a plasma reactor having a small antenna-to-workpiece gap, in order tominimize the decrease in plasma ion density near the center region ofthe workpiece corresponding to the inductive antenna pattern centernull, it is an object of the invention to increase the magnitude of theinduced electric field at the center region. The invention accomplishesthis by concentrating the turns of an inductive coil overlying theceiling near the axis of symmetry of the antenna and maximizing the rateof change (at the RF source frequency) of magnetic flux linkage betweenthe antenna and the plasma in that center region.

In accordance with the invention, a solenoidal coil around the symmetryaxis simultaneously concentrates its inductive coil turns near the axisand maximizes the rate of change of magnetic flux linkage between theantenna and the plasma in the center region adjacent the workpiece. Thisis because the number of turns is large and the coil radius is small, asrequired for strong flux linkage and close mutual coupling to the plasmain the center region. (In contrast, a conventional planar coil antennaspreads its inductive field over a wide radial area, pushing the radialpower distribution outward toward the periphery.) As understood in thisspecification, a solenoid-like antenna is one which has plural inductiveelements distributed in a non-planar manner relative to a plane of theworkpiece or workpiece support surface or overlying chamber ceiling, orspaced at different distances transversely to the workpiece supportplane (defined by a workpiece supporting pedestal within the chamber) orspaced at different distances transversely to an overlying chamberceiling. As understood in this specification, an inductive element is acurrent-carrying element mutually inductively coupled with the plasma inthe chamber and/or with other inductive elements of the antenna.

A preferred embodiment of the invention includes dual solenoidal coilantennas with one solenoid near the center and another one at an outerperipheral radius. The two solenoids may be driven at different RFfrequencies or at the same frequency, in which case they are preferablyphase-locked and more preferably phase-locked in such a manner thattheir fields constructively interact. The greatest practicaldisplacement between the inner and outer solenoid is preferred becauseit provides the most versatile control of etch rate at the workpiececenter relative to etch rate at the workpiece periphery. The skilledworker may readily vary RF power, chamber pressure andelectro-negativity of the process gas mixture (by choosing theappropriate ratio of molecular and inert gases) to obtain a wider rangeor process window in which to optimize (using the present invention) theradial uniformity of the etch rate across the workpiece. Maximum spacingbetween the separate inner and outer solenoids of the preferredembodiment provides the following advantages:

(1) maximum uniformity control and adjustment;

(2) maximum isolation between the inner and outer solenoids, preventinginterference of the field from one solenoid with that of the other; and

(3) maximum space on the ceiling (between the inner and outer solenoids)for temperature control elements to optimize ceiling temperaturecontrol.

FIG. 4A illustrates a single solenoid embodiment (not the preferredembodiment) of an inductively coupled RF plasma reactor having a shortworkpiece-to-ceiling gap, meaning that the skin depth of the inductionfield is on the order of the gap length. As understood in thisspecification, a skin depth which is on the order of the gap length isthat which is within a factor of ten of (i.e., between about one tenthand about ten times) the gap length.

FIG. 5 illustrates a dual solenoid embodiment of an inductively coupledRF plasma reactor, and is the preferred embodiment of the invention.Except for the dual solenoid feature, the reactor structure of theembodiments of FIGS. 4A and 5 is nearly the same, and will now bedescribed with reference to FIG. 4A. The reactor includes a cylindricalchamber 40 similar to that of FIG. 1, except that the reactor of FIG. 4Ahas a non-planar coil antenna 42 whose windings 44 are closelyconcentrated in non-planar fashion near the antenna symmetry axis 46.While in the illustrated embodiment the windings 44 are symmetrical andtheir symmetry axis 46 coincides with the center axis of the chamber,the invention may be carried out differently. For example, the windingsmay not be symmetrical and/or their axis of symmetry may not coincide.However, in the case of a symmetrical antenna, the antenna has aradiation pattern null near its symmetry axis 46 coinciding with thecenter of the chamber or the workpiece center. Close concentration ofthe windings 44 about the center axis 46 compensates for this null andis accomplished by vertically stacking the windings 44 in the manner ofa solenoid so that they are each a minimum distance from the chambercenter axis 46. This increases the product of current (I) and coil turns(N) near the chamber center axis 46 where the plasma ion density hasbeen the weakest for short workpiece-to-ceiling heights, as discussedabove with reference to FIGS. 3D and 3E. As a result, the RF powerapplied to the non-planar coil antenna 42 produces greater induction[d/dt][N•] at the wafer center--at the antenna symmetry axis46--(relative to the peripheral regions) and therefore produces greaterplasma ion density in that region, so that the resulting plasma iondensity is more nearly uniform despite the small workpiece-to-ceilingheight. Thus, the invention provides a way for reducing the ceilingheight for enhanced plasma process performance without sacrificingprocess uniformity.

The drawing of FIG. 4B best shows a preferred implementation of thewindings employed in the embodiments of FIGS. 4A and 5. In order thatthe windings 44 be at least nearly parallel to the plane of theworkpiece 56, they preferably are not wound in the usual manner of ahelix but, instead, are preferably wound so that each individual turn isparallel to the (horizontal) plane of the workpiece 56 except at a stepor transition 44a between turns (from one horizontal plane to the next).

The cylindrical chamber 40 consists of a cylindrical side wall 50 and acircular ceiling 52 integrally formed with the side wall 50 so that theside wall 50 and ceiling 52 constitute a single piece of material, suchas silicon. However, the invention may be carried out with the side wall50 and ceiling 52 formed as separate pieces, as will be described laterin this specification. The circular ceiling 52 may be of any suitablecross-sectional shape such as planar (FIG. 4A), dome (FIG. 4C), conical(FIG. 4D), truncated conical (FIG. 4E), cylindrical or any combinationof such shapes or curve of rotation. Such a combination will bediscussed later in this specification. Generally, the vertical pitch ofthe solenoid 42 (i.e., its vertical height divided by its horizontalwidth) exceeds the vertical pitch of the ceiling 52, even for ceilingsdefining 3-dimensional surfaces such as dome, conical, truncated conicaland so forth. The purpose for this, at least in the preferredembodiment, is to concentrate the induction of the antenna near theantenna symmetry axis, as discussed previously in this specification. Asolenoid having a pitch exceeding that of the ceiling is referred toherein as a non-conformal solenoid, meaning that, in general, its shapedoes not conform with the shape of the ceiling, and more specificallythat its vertical pitch exceeds the vertical pitch of the ceiling. A2-dimensional or flat ceiling has a vertical pitch of zero, while a3-dimensional ceiling has a non-zero vertical pitch.

A pedestal 54 at the bottom of the chamber 40 supports a planarworkpiece 56 in a workpiece support plane during processing. Theworkpiece 56 is typically a semiconductor wafer and the workpiecesupport plane is generally the plane of the wafer or workpiece 56. Thechamber 40 is evacuated by a pump (not shown in the drawing) through anannular passage 58 to a pumping annulus 60 surrounding the lower portionof the chamber 40. The interior of the pumping annulus may be lined witha replaceable metal liner 60a. The annular passage 58 is defined by thebottom edge 50a of the cylindrical side wall 50 and a planar ring 62surrounding the pedestal 54. Process gas is furnished into the chamber40 through any one or all of a variety of gas feeds. In order to controlprocess gas flow near the workpiece center, a center gas feed 64a canextend downwardly through the center of the ceiling 52 toward the centerof the workpiece 56 (or the center of the workpiece support plane). Inorder to control gas flow near the workpiece periphery (or near theperiphery of the workpiece support plane), plural radial gas feeds 64b,which can be controlled independently of the center gas feed 64a, extendradially inwardly from the side wall 50 toward the workpiece periphery(or toward the workpiece support plane periphery), or base axial gasfeeds 64c extend upwardly from near the pedestal 54 toward the workpieceperiphery, or ceiling axial gas feeds 64d can extend downwardly from theceiling 52 toward the workpiece periphery. Etch rates at the workpiececenter and periphery can be adjusted independently relative to oneanother to achieve a more radially uniform etch rate distribution acrossthe workpiece by controlling the process gas flow rates toward theworkpiece center and periphery through, respectively, the center gasfeed 64a and any one of the outer gas feeds 64b-d. This feature of theinvention can be carried out with the center gas feed 64a and only oneof the peripheral gas feeds 64b-d.

The solenoidal coil antenna 42 is wound around a housing 66 surroundingthe center gas feed 64. A plasma source RF power supply 68 is connectedacross the coil antenna 42 and a bias RF power supply 70 is connected tothe pedestal 54.

Confinement of the overhead coil antenna 42 to the center region of theceiling 52 leaves a large portion of the top surface of the ceiling 52unoccupied and therefore available for direct contact with temperaturecontrol apparatus including, for example, plural radiant heaters 72 suchas tungsten halogen lamps and a water-cooled cold plate 74 which may beformed of copper or aluminum for example, with coolant passages 74aextending therethrough. Preferably the coolant passages 74a contain acoolant of a known variety having a high thermal conductivity but a lowelectrical conductivity, to avoid electrically loading down the antennaor solenoid 42. The cold plate 74 provides constant cooling of theceiling 52 while the maximum power of the radiant heaters 72 is selectedso as to be able to overwhelm, if necessary, the cooling by the coldplate 74, facilitating responsive and stable temperature control of theceiling 52. The large ceiling area irradiated by the heaters 72 providesgreater uniformity and efficiency of temperature control. (It should benoted that radiant heating is not necessarily required in carrying outthe invention, and the skilled worker may choose to employ an electricheating element instead, as will be described later in thisspecification.) If the ceiling 52 is silicon, as disclosed in co-pendingU.S. application Ser. No. 08/597,577 filed Feb. 2, 1996 by Kenneth S.Collins et al., then there is a significant advantage to be gained bythus increasing the uniformity and efficiency of the temperature controlacross the ceiling. Specifically, where a polymer precursor and etchantprecursor process gas (e.g., a fluorocarbon gas) is employed and whereit is desirable to scavenge the etchant (e.g., fluorine), the rate ofpolymer deposition across the entire ceiling 52 and/or the rate at whichthe ceiling 52 furnishes a fluorine etchant scavenger material (silicon)into the plasma is better controlled by increasing the contact area ofthe ceiling 52 with the temperature control heater 72. The solenoidantenna 42 increases the available contact area on the ceiling 52because the solenoid windings 44 are concentrated at the center axis ofthe ceiling 52.

The increase in available area on the ceiling 52 for thermal contact isexploited in a preferred implementation by a highly thermally conductivetorus 75 (formed of a ceramic such as aluminum nitride, aluminum oxideor silicon nitride or of a non-ceramic like silicon or silicon carbideeither lightly doped or undoped) whose bottom surface rests on theceiling 52 and whose top surface supports the cold plate 74. One featureof the torus 75 is that it displaces the cold plate 74 well-above thetop of the solenoid 42. This feature substantially mitigates or nearlyeliminates the reduction in inductive coupling between the solenoid 42and the plasma which would otherwise result from a close proximity ofthe conductive plane of the cold plate 74 to the solenoid 42. In orderto prevent such a reduction in inductive coupling, it is preferable thatthe distance between the cold plate 74 and the top winding of thesolenoid 42 be at least a substantial fraction (e.g., one half) of thetotal height of the solenoid 42. Plural axial holes 75a extendingthrough the torus 75 are spaced along two concentric circles and holdthe plural radiant heaters or lamps 72 and permit them to directlyirradiate the ceiling 52. For greatest lamp efficiency, the holeinterior surface may be lined with a reflective (e.g., aluminum) layer.The center gas feed 64a of FIG. 4 may be replaced by a radiant heater 72(as shown in FIG. 5), depending upon the particular reactor design andprocess conditions. The ceiling temperature is sensed by a sensor suchas a thermocouple 76 extending through one of the holes 75a not occupiedby a lamp heater 72. For good thermal contact, a highly thermallyconductive elastomer 73 such as silicone rubber impregnated with boronnitride is placed between the ceramic torus 75 and the copper cold plate74 and between the ceramic torus 75 and the silicon ceiling 52.

As disclosed in the above-referenced co-pending application, the chamber40 may be an all-semiconductor chamber, in which case the ceiling 52 andthe side wall 50 are both a semiconductor material such as silicon orsilicon carbide. As described in the above-referenced co-pendingapplication, controlling the temperature of, and RF bias power appliedto, either the ceiling 52 or the wall 50 regulates the extent to whichit furnishes fluorine scavenger precursor material (silicon) into theplasma or, alternatively, the extent to which it is coated with polymer.The material of the ceiling 52 is not limited to silicon but may be, inthe alternative, silicon carbide, silicon dioxide (quartz), siliconnitride, aluminum nitride or a ceramic such as aluminum oxide.

As described in the above-referenced co-pending application, the chamberwall or ceiling 50, 52 need not be used as the source of a fluorinescavenger material. Instead, a disposable semiconductor (e.g., siliconor silicon carbide) member can be placed inside the chamber 40 andmaintained at a sufficiently high temperature to prevent polymercondensation thereon and permit silicon material to be removed therefrominto the plasma as fluorine scavenging material. In this case, the wall50 and ceiling 52 need not necessarily be silicon, or if they aresilicon they may be maintained at a temperature (and/or RF bias) near orbelow the polymer condensation temperature (and/or a polymercondensation RF bias threshold) so that they are coated with polymerfrom the plasma so as to be protected from being consumed. While thedisposable silicon member may take any appropriate form, in theembodiment of FIG. 4 the disposable silicon member is an annular ring 62surrounding the pedestal 54. Preferably, the annular ring 62 is highpurity silicon and may be doped to alter its electrical or opticalproperties. In order to maintain the silicon ring 62 at a sufficienttemperature to ensure its favorable participation in the plasma process(e.g., its contribution of silicon material into the plasma for fluorinescavenging), plural radiant (e.g., tungsten halogen lamp) heaters 77arranged in a circle under the annular ring 62 heat the silicon ring 62through a quartz window 78. As described in the above-referencedco-pending application, the heaters 77 are controlled in accordance withthe measured temperature of the silicon ring 62 sensed by a temperaturesensor 79 which may be a remote sensor such as an optical pyrometer or afluoro-optical probe. The sensor 79 may extend partially into a verydeep hole 62a in the ring 62, the deepness and narrowness of the holetending at least partially to mask temperature-dependent variations inthermal emissivity of the silicon ring 62, so that it behaves more likea gray-body radiator for more reliable temperature measurement.

As described in U.S. application Ser. No. 08/597,577 referred to above,an advantage of an all-semiconductor chamber is that the plasma is freeof contact with contaminant producing materials such as metal, forexample. For this purpose, plasma confinement magnets 80, 82 adjacentthe annular opening 58 prevent or reduce plasma flow into the pumpingannulus 60. To the extent any polymer precursor and/or active speciessucceeds in entering the pumping annulus 60, any resulting polymer orcontaminant deposits on the replaceable interior liner 60a may beprevented from re-entering the plasma chamber 40 by maintaining theliner 60a at a temperature significantly below the polymer condensationtemperature, for example, as disclosed in the referenced co-pendingapplication.

A wafer slit valve 84 through the exterior wall of the pumping annulus60 accommodates wafer ingress and egress. The annular opening 58 betweenthe chamber 40 and pumping annulus 60 is larger adjacent the wafer slitvalve 84 and smallest on the opposite side by virtue of a slant of thebottom edge of the cylindrical side wall 50 so as to make the chamberpressure distribution more symmetrical with a non-symmetrical pump portlocation.

Maximum mutual inductance near the chamber center axis 46 is achieved bythe vertically stacked solenoidal windings 44. In the embodiment of FIG.4, another winding 45 outside of the vertical stack of windings 44 butin the horizontal plane of the bottom solenoidal winding 44a may beadded, provided the additional winding 45 is close to the bottomsolenoidal winding 44a.

Referring specifically now to the preferred dual solenoid embodiment ofFIG. 5, a second outer vertical stack or solenoid 120 of windings 122 atan outer location (i.e, against the outer circumferential surface of thethermally conductive torus 75) is displaced by a radial distance δR fromthe inner vertical stack of solenoidal windings 44. Note that in FIG. 5confinement of the inner solenoidal antenna 42 to the center and theouter solenoidal antenna 120 to the periphery leaves a large portion ofthe top surface of the ceiling 52 available for direct contact with thetemperature control apparatus 72, 74, 75, as in FIG. 4A. An advantage isthat the larger surface area contact between the ceiling 52 and thetemperature control apparatus provides a more efficient and more uniformtemperature control of the ceiling 52.

For a reactor in which the side wall and ceiling are formed of a singlepiece of silicon for example with an inside diameter of 12.6 in (32 cm),the wafer-to-ceiling gap is 3 in (7.5 cm), and the mean diameter of theinner solenoid was 3.75 in (9.3 cm) while the mean diameter of the outersolenoid was 11.75 in (29.3 cm) using 3/16 in diameter hollow coppertubing covered with a 0.03 thick teflon insulation layer, each solenoidconsisting of four turns and being 1 in (2.54 cm) high. The outer stackor solenoid 120 is energized by a second independently controllableplasma source RF power supply 96. The purpose is to permit differentuser-selectable plasma source power levels to be applied at differentradial locations relative to the workpiece or wafer 56 to permitcompensation for known processing non-uniformities across the wafersurface, a significant advantage. In combination with the independentlycontrollable center gas feed 64a and peripheral gas feeds 64b-d, etchperformance at the workpiece center may be adjusted relative to etchperformance at the edge by adjusting the RF power applied to the innersolenoid 42 relative to that applied to the outer solenoid 90 andadjusting the gas flow rate through the center gas feed 64a relative tothe flow rate through the outer gas feeds 64b-d. While the presentinvention solves or at least ameliorates the problem of a center null ordip in the inductance field as described above, there may be otherplasma processing non-uniformity problems, and these can be compensatedin the versatile embodiment of FIG. 5 by adjusting the relative RF powerlevels applied to the inner and outer antennas. For effecting thispurpose with greater convenience, the respective RF power supplies 68,96 for the inner and outer solenoids 42, 90 may be replaced by a commonpower supply 97a and a power splitter 97b which permits the user tochange the relative apportionment of power between the inner and outersolenoids 42, 90 while preserving a fixed phase relationship between thefields of the inner and outer solenoids 42, 90. This is particularlyimportant where the two solenoids 42, 90 receive RF power at the samefrequency. Otherwise, if the two independent power supplies 68, 96 areemployed, then they may be powered at different RF frequencies, in whichcase it is preferable to install RF filters at the output of each RFpower supply 68, 96 to avoid off-frequency feedback from couplingbetween the two solenoids. In this case, the frequency difference shouldbe sufficient to time-average out coupling between the two solenoidsand, furthermore, should exceed the rejection bandwidth of the RFfilters. A preferred mode is to make each frequency independentlyresonantly matched to the respective solenoid, and each frequency may bevaried to follow changes in the plasma impedance (thereby maintainingresonance) in lieu of conventional impedance matching techniques. Inother words, the RF frequency applied to the antenna is made to followthe resonant frequency of the antenna as loaded by the impedance of theplasma in the chamber. In such implementations, the frequency ranges ofthe two solenoids should be mutually exclusive. In an alternative mode,the two solenoids are driven at the same RF frequency and in this caseit is preferable that the phase relationship between the two be such asto cause constructive interaction or superposition of the fields of thetwo solenoids. Generally, this requirement will be met by a zero phaseangle between the signals applied to the two solenoids if they are bothwound in the same sense. Otherwise, if they are oppositely wound, thephase angle is preferably 180°. In any case, coupling between the innerand outer solenoids can be minimized or eliminated by having arelatively large space between the inner and outer solenoids 42, 90, aswill be discussed below in this specification.

The range attainable by such adjustments is increased by increasing theradius of the outer solenoid 90 to increase the spacing between theinner and outer solenoids 42, 90, so that the effects of the twosolenoids 42, 90 are more confined to the workpiece center and edge,respectively. This permits a greater range of control in superimposingthe effects of the two solenoids 42, 90. For example, the radius of theinner solenoid 42 should be no greater than about half the workpieceradius and preferably no more than about a third thereof. (The minimumradius of the inner solenoid 42 is affected in part by the diameter ofthe conductor forming the solenoid 42 and in part by the need to providea finite non-zero circumference for an arcuate--e.g., circular--currentpath to produce inductance.) The radius of the outer coil 90 should beat least equal to the workpiece radius and preferably 1.5 or more timesthe workpiece radius. With such a configuration, the respective centerand edge effects of the inner and outer solenoids 42, 90 are sopronounced that by increasing power to the inner solenoid the chamberpressure can be raised into the hundreds of mT while providing a uniformplasma, and by increasing power to the outer solenoid 90 the chamberpressure can be reduced to on the order of 0.01 mT while providing auniform plasma. Another advantage of such a large radius of the outersolenoid 90 is that it minimizes coupling between the inner and outersolenoids 42, 90.

FIG. 5 indicates in dashed line that a third solenoid may be added as anoption, which is desirable for a very large chamber diameter.

FIG. 6 illustrates a variation of the embodiment of FIG. 5 in which theouter solenoid 90 is replaced by a planar winding 100.

FIG. 7A illustrates a variation of the embodiment of FIG. 4 in which thecenter solenoidal winding includes not only the vertical stack 42 ofwindings 44 but in addition a second vertical stack 102 of windings 104closely adjacent to the first stack 42 so that the two stacks constitutea double-wound solenoid 106. Referring to FIG. 7B, the doubly woundsolenoid 106 may consist of two independently wound single solenoids 42,102, the inner solenoid 42 consisting of the windings 44a, 44b, and soforth and the outer solenoid 102 consisting of the winding 104a, 104band so forth. Alternatively, referring to FIG. 7C, the doubly woundsolenoid 106 may consist of vertically stacked pairs of at least nearlyco-planar windings. In the alternative of FIG. 7C, each pair of nearlyco-planar windings (e.g., the pair 44a, 104a or the pair 44b, 104b) maybe formed by helically winding a single conductor. The term "doublywound" used herein refers to winding of the type shown in either FIG. 7Bor 7C. In addition, the solenoid winding may not be merely doubly woundbut may be triply wound or more and in general it can consists of pluralwindings at each plane along the axis of symmetry. Such multiple-woundsolenoids may be employed in either one or both the inner and outersolenoids 42, 90 of the dual-solenoid embodiment of FIG. 5.

FIG. 8 illustrates a variation of the embodiment of FIG. 7A in which anouter doubly wound solenoid 110 concentric with the inner doubly woundsolenoid 106 is placed at a radial distance δR from the inner solenoid106.

FIG. 9 illustrates a variation of the embodiment of FIG. 8 in which theouter doubly wound solenoid 110 is replaced by an ordinary outersolenoid 112 corresponding to the outer solenoid employed in theembodiment of FIG. 5.

FIG. 10 illustrates another preferred embodiment in which the solenoid42 of FIG. 5 is placed at a location displaced by a radial distance δrfrom the center gas feed housing 66. In the embodiment of FIG. 4, δr iszero while in the embodiment of FIG. 10 δr is a significant fraction ofthe radius of the cylindrical side wall 50. Increasing δr to the extentillustrated in FIG. 10 may be helpful as an alternative to theembodiments of FIGS. 4, 5, 7 and 8 for compensating for non-uniformitiesin addition to the usual center dip in plasma ion density described withreference to FIGS. 3D and 3E. Similarly, the embodiment of FIG. 10 maybe helpful where placing the solenoid 42 at the minimum distance fromthe chamber center axis 46 (as in FIG. 4) would so increase the plasmaion density near the center of the wafer 56 as to over-correct for theusual dip in plasma ion density near the center and create yet anothernon-uniformity in the plasma process behavior. In such a case, theembodiment of FIG. 10 is preferred where δr is selected to be an optimumvalue which provides the greatest uniformity in plasma ion density.Ideally in this case, δr is selected to avoid both under-correction andover-correction for the usual center dip in plasma ion density. Thedetermination of the optimum value for δr can be carried out by theskilled worker by trial and error steps of placing the solenoid 42 atdifferent radial locations and employing conventional techniques todetermine the radial profile of the plasma ion density at each step.

FIG. 11 illustrates an embodiment in which the solenoid 42 has aninverted conical shape while FIG. 12 illustrates an embodiment in whichthe solenoid 42 has an upright conical shape.

FIG. 13 illustrates an embodiment in which the solenoid 42 is combinedwith a planar helical winding 120. The planar helical winding has theeffect of reducing the severity with which the solenoid winding 42concentrates the induction field near the center of the workpiece bydistributing some of the RF power somewhat away from the center. Thisfeature may be useful in cases where it is necessary to avoidover-correcting for the usual center null. The extent of such diversionof the induction field away from the center corresponds to the radius ofthe planar helical winding 120. FIG. 14 illustrates a variation of theembodiment of FIG. 13 in which the solenoid 42 has an inverted conicalshape as in FIG. 11. FIG. 15 illustrates another variation of theembodiment of FIG. 13 in which the solenoid 42 has an upright conicalshape as in the embodiment of FIG. 12.

The RF potential on the ceiling 52 may be increased, for example toprevent polymer deposition thereon, by reducing its effective capacitiveelectrode area relative to other electrodes of the chamber (e.g., theworkpiece and the sidewalls). FIG. 16 illustrates how this can beaccomplished by supporting a smaller-area version of the ceiling 52' onan outer annulus 200, from which the smaller-area ceiling 52' isinsulated. The annulus 200 may be formed of the same material (e.g.,silicon) as the ceiling 52' and may be of a truncated conical shape(indicated in solid line) or a truncated dome shape (indicated in dashedline). A separate RF power supply 205 may be connected to the annulus200 to permit more workpiece center versus edge process adjustments.

FIG. 17A illustrates a variation of the embodiment of FIG. 5 in whichthe ceiling 52 and side wall 50 are separate semiconductor (e.g.,silicon) pieces insulated from one another having separately controlledRF bias power levels applied to them from respective RF sources 210, 212to enhance control over the center etch rate and selectivity relative tothe edge. As set forth in greater detail in above-referenced U.S.application Ser. No. 08/597,577 filed Feb. 2, 1996 by Kenneth S. Collinset al., the ceiling 52 may be a semiconductor (e.g., silicon) materialdoped so that it will act as an electrode capacitively coupling the RFbias power applied to it into the chamber and simultaneously as a windowthrough which RF power applied to the solenoid 42 may be inductivelycoupled into the chamber. The advantage of such a window-electrode isthat an RF potential may be established directly over the wafer (e.g.,for controlling ion energy) while at the same time inductively couplingRF power directly over the wafer. This latter feature, in combinationwith the separately controlled inner and outer solenoids 42, 90 andcenter and peripheral gas feeds 64a, 64b greatly enhances the ability toadjust various plasma process parameters such as ion density, ionenergy, etch rate and etch selectivity at the workpiece center relativeto the workpiece edge to achieve an optimum uniformity. In thiscombination, gas flow through individual gas feeds is individually andseparately controlled to achieve such optimum uniformity of plasmaprocess parameters.

FIG. 17A illustrates how the lamp heaters 72 may be replaced by electricheating elements 72'. As in the embodiment of FIG. 4, the disposablesilicon member is an annular ring 62 surrounding the pedestal 54.Preferably, the annular ring 62 is high purity silicon and may be dopedto alter its electrical or optical properties. In order to maintain thesilicon ring 62 at a sufficient temperature to ensure its favorableparticipation in the plasma process (e.g., its contribution of siliconmaterial into the plasma for fluorine scavenging), plural radiant (e.g.,tungsten halogen lamp) heaters 77 arranged in a circle under the annularring 62 heat the silicon ring 62 through a quartz window 78. Asdescribed in the above-referenced co-pending application, the heaters 77are controlled in accordance with the measured temperature of thesilicon ring 62 sensed by a temperature sensor 79 which may be a remotesensor such as an optical pyrometer or a fluoro-optical probe. Thesensor 79 may extend partially into a very deep hole 62a in the ring 62,the deepness and narrowness of the hole tending at least partially tomask temperature-dependent variations in thermal emissivity of thesilicon ring 62, so that it behaves more like a gray-body radiator formore reliable temperature measurement.

FIG. 17B illustrates another variation in which the ceiling 52 itselfmay be divided into an inner disk 52a and an outer annulus 52belectrically insulated from one another and separately biased byindependent RF power sources 214, 216 which may be separate outputs of asingle differentially controlled RF power source.

In accordance with an alternative embodiment, a user-accessible centralcontroller 300 shown in FIGS. 17A and 17B, such as a programmableelectronic controller including, for example, a conventionalmicroprocessor and memory, is connected to simultaneously control gasflow rates through the central and peripheral gas feeds 64a, 64, RFplasma source power levels applied to the inner and outer antennas 42,90 and RF bias power levels applied to the ceiling 52 and side wall 50respectively (in FIG. 17A) and the RF bias power levels applied to theinner and outer ceiling portions 52a, 52b (in FIG. 17B), temperature ofthe ceiling 52 and the temperature of the silicon ring 62. A ceilingtemperature controller 218 governs the power applied by a lamp powersource 220 to the heater lamps 72' by comparing the temperature measuredby the ceiling temperature sensor 76 with a desired temperature known tothe controller 300. A ring temperature controller 222 controls the powerapplied by a heater power source 224 to the heater lamps 77 facing thesilicon ring 62 by comparing the ring temperature measured by the ringsensor 79 with a desired ring temperature stored known to the controller222. The master controller 300 governs the desired temperatures of thetemperature controllers 218 and 222, the RF power levels of the solenoidpower sources 68, 96, the RF power levels of the bias power sources 210,212 (FIG. 17A) or 214, 216 (FIG. 17B), the wafer bias level applied bythe RF power source 70 and the gas flow rates supplied by the variousgas supplies (or separate valves) to the gas inlets 64a-d. The key tocontrolling the wafer bias level is the RF potential difference betweenthe wafer pedestal 54 and the ceiling 52. Thus, either the pedestal RFpower source 70 or the ceiling RF power source 212 may be simply a shortto RF ground. With such a programmable integrated controller, the usercan easily optimize apportionment of RF source power, RF bias power andgas flow rate between the workpiece center and periphery to achieve thegreatest center-to-edge process uniformity across the surface of theworkpiece (e.g., uniform radial distribution of etch rate and etchselectivity). Also, by adjusting (through the controller 300) the RFpower applied to the solenoids 42, 90 relative to the RF powerdifference between the pedestal 54 and ceiling 52, the user can operatethe reactor in a predominantly inductively coupled mode or in apredominantly capacitively coupled mode.

While the various power sources connected in FIG. 17A to the solenoids42, 90, the ceiling 52, side wall 50 (or the inner and outer ceilingportions 52a, 52b as in FIG. 17B) have been described as operating at RFfrequencies, the invention is not restricted to any particular range offrequencies, and frequencies other than RF may be selected by theskilled worker in carrying out the invention.

In a preferred embodiment of the invention, the high thermalconductivity spacer 75, the ceiling 52 and the side wall 50 areintegrally formed together from a single piece of crystalline silicon.

DETAILED DESCRIPTION RELATING TO THE PRESENT INVENTION

Referring again to FIG. 5, a preferred plasma processing chamberincludes a window/electrode 52. The window/electrode 52 is fabricatedfrom semiconducting material as described in detail in theabove-referenced applications so that it may function as both a windowto RF electromagnetic or inductive power coupling from one or moreexternal (outside chamber) antennas or coils to the plasma within thechamber and as an electrode for electrostatically or capacitivelycoupling RF power to the plasma within the chamber (or for terminatingor providing a ground or return path for such capacitive orelectrostatic coupling of RF power) or for biasing the workpiece orwafer.

The window/electrode 52 may be any shape as described in theabove-referenced applications, but in this example is approximately aflat disc which may optionally include a cylindrical wall or skirtextending outward from the disk, such as for plasma confinement asdescribed in the above-referenced applications.

The window/electrode 52 is interfaced to the heat sink 74 through theheat transfer material 75. Typically the heat sink 74 is a water cooledmetal plate, preferably a good thermal conductor such as aluminum orcopper, but may optionally be a non-metal. The heat sink 74 typically acooling apparatus preferably of the type which uses a liquid coolantsuch as water or ethylene-glycol that is forced through cooling passagesof sufficient surface area within the heat sink 74 by a closed-loop heatexchanger or chiller. The liquid flow rate or temperature may bemaintained approximately constant. Alternatively, the liquid flow rateor temperature may be an output variable of the temperature controlsystem.

Preferably, radiant heating is used to apply heat to thewindow/electrode. The radiant heaters 72 are a plurality of tungstenfilament lamps utilizing a quartz envelope filled with a mixture ofhalogen and inert gases. Radiant heaters are preferred to other heatertypes because thermal lag is minimized: The thermal capacitance of atungsten filament lamp is very low, such that the time response offilament temperature (and thus of power output) to a change in powersetting is short (<1 second), and since the heat transfer mechanismbetween lamp filament and load is by radiation, the total thermal lagfor heating is minimized. In addition, since the heat transfer mechanismbetween lamp filament and load is by radiation, the total thermal lagfor heating is minimized. In addition, since the thermal capacitance ofa tungsten filament lamp is very low, the amount of stored thermalenergy in the lamp is very low, and when a reduction in heating power iscalled for by the control system, the filament temperature may bequickly dropped and the lamp output power thus also quickly drops. Asshown in FIG. 5, the lamps 72 directly radiate the load (thewindow/electrode 52) for the fastest possible response. However,alternatively, the lamps 72 may radiate the heat transfer material 75.Lamp heating may be provided in more than one zone, i.e. lamps at two ormore radii from the axis of the window/electrode to improve thermaluniformity of window/electrode. For maximum thermal uniformity, lamps inthe two or more zones may be provided with separate control, each zoneutilizing its own temperature measurement, control system, and outputtransducer. This is especially useful when the heat flux spatialdistribution from inside the chamber varies depending on processparameters, processes, process sequences, or other boundary conditions.

The heat transfer material 75 may be formed integrally with thewindow/electrode 52 that is formed of the same material into a singlepiece structure for elimination of a thermal contact resistance thatwould be present if heat transfer material 75 and window/electrode 52were two separate parts. Alternatively, the heat transfer material 75and the window/electrode 52 may be two parts of same or differentmaterials that are bonded together, (preferably with a high electricalresistivity material since the window/electrode 52 is used for inductiveor electromagnetic coupling of RF or microwave power using inductiveantennas 90, 92 and/or 42, 44), minimizing the thermal contactresistance between the heat transfer material 75 and thewindow/electrode 52.

Alternatively, the heat transfer material 75 and the window/electrode 52may be two parts of same or different materials that are interfacedtogether through a contact resistance. In this case, the heat transfermaterial 75 is preferably made of a highly thermally conductive materialof high electrical resistivity. Additionally, a low product of densityand specific heat are preferred. SiC, Si, AIN, and AI₂ O₃ are examples.

Properties of SiC are indicated below:

Thermal conductivity: 130 watt/meter*Kelvin

Electrical resistivity: >10⁵ ohm*cm

Specific Heat: 0.66 joule/gram*Kelvin

Density: 3.2 gram/cm³

Silicon may also be used, if lightly (not heavily) doped (i.e. 10¹⁴/cm³) and has the following properties:

Thermal conductivity: 80 watt/meter*Kelvin

Electrical resistivity: 20-100 ohm*cm

Specific Heat: 0.7 joule/gram*Kelvin

Density: 2.3 gram/cm³

Aluminum nitride or aluminum oxide are other alternatives.

The heat transfer material 75 may be bonded to the heat sink 74 bytechniques well known in the art (e.g., using bonding materials such asthermoplastics, epoxies, or other organic or inorganic bondingmaterials), without the restriction of requiring high electricalresistivity bonding material in the area proximate the heat sink 74.This provides a very low thermal contact resistance between heattransfer material 75 and heat sink 74.

The heat transfer material 75 also serves to separate the inductiveantennas 90, 92 and/or 42, 44 from the heat sink 74 which if it ismetal, forms a ground plane or reflector to the induction fieldgenerated in the vicinity of each inductive antenna 90, 92 and/or 42,44. If the heat sink 74 is metal and is too close to the inductiveantenna 90, 92 and/or 42, 44, then eddy currents are induced in theground plane, causing power loss. In addition, the RF currents throughthe antenna 90, 92 and/or 42, 44 become very large to drive a given RFpower, increasing I² R losses in the circuit. The antennas 90, 92 and/or42, 44 are each four turns comprised of 3/16" diameter water cooledcopper tubing insulated with 1/4" outside diameter teflon tubingyielding coils 1" in height. An acceptable distance between thewindow/electrode 52 and the metal heat sink 74 is about 2", yieldingabout a 1" distance between the top of the antenna 90, 92 and/or 42, 44and the heat sink 74.

As described above, thermal contact resistances between the heattransfer material 75 and the window, electrode 52, and between the heattransfer material 75 and the heat sink 74 can be minimized by bondingthe materials together. Also described above was an example of formingthe window/electrode 52 and the heat transfer material 75 from a singlepiece of material, eliminating one thermal contact resistance. However,in some cases, one or both thermal contact resistances cannot beavoided. However, the thermal contact resistance(s) can be minimized inaccordance with a feature of the present invention, which will now beintroduced.

Thermal contact resistance between two parts is comprised of twoparallel elements: 1) mechanical point contact between the parts, and 2)conduction through air (or other medium) between the parts. In theabsence of air or other medium, the thermal contact resistance betweenthe two parts is very high and typically unacceptable for heating and/orcooling of the window/electrode 52 due to the high heat loads imposed onit during typical plasma reactor operation. The presence of air yields alower thermal contact resistance than mechanical point contact alone,but is typically marginal depending on the effective gap between parts,which is a function of the surface roughness and flatness of both parts.For air in the high pressure continuum regime wherein the mean-free-pathin the gas is small relative to the effective gap between parts, thethermal conductivity of the air is invariant with gas pressure, and thethermal conductance per unit area is simply the ratio of the thermalconductivity of air to the effective gap. For air at atmosphericpressure and 100 degrees C., the thermal conductivity is about 0.03watt/meter*Kelvin. Heat transfer across the gap is limited by the lowchamber pressure and by the fact that the mechanical contact between thetwo parts is only point contact.

In order to improve heat transfer, a thermally conductive gas such as(preferably) helium or another one of the inert gases such as argon,xenon and so forth, can be placed in the gap between the between theheat transfer material 75 and the heat sink 74 and/or in the gap betweenthe heat transfer material 75 and the window/electrode 52, in accordancewith a first embodiment of the present invention. The thermallyconductive gas in the gap is best pressurized above the chamber pressureto as high as atmospheric pressure, although preferably the pressure ofthe thermal transfer gas in the gap is between the chamber pressure andatmospheric pressure. Helium is a preferred choice for the thermallyconductive gas because helium has a thermal conductivity of about 0.18watt/meter*Kelvin at atmospheric pressure and 100 degree C. To minimizethermal contact resistance between the heat transfer material 75 and theheat sink 74, helium can be provided to each interface therebetweenthrough a helium distribution manifold within the heat sink 74, as willbe described in detail below in this specification. As will also bedescribed below in detail, an O-ring of small cross-section and lowdurometer can be used to reduce helium leakage and between heat transfermaterial 75 and heat sink 74. Through-holes from the top surface of theheat transfer material or rings 75 can connect a helium passage from anupper interface between the heat sink 74 and the heat transfer materialring 75, to interface between the heat transfer material ring 75 and thewindow/electrode 52. Helium can be supplied to the aforementioned heliumdistribution manifold located within heat sink 74 at a pressure somewhatabove atmospheric to minimize dilution of helium by air which couldotherwise increase the thermal contact resistance.

Other materials may be used in between the heat transfer material 75 andthe window/electrode 52, and between the heat transfer material 75 andthe heat sink 74 to minimize thermal contact resistances. Examples arethermally conductive, compliant elastomeric pads such as boron nitrideor silicon carbide or silicon or aluminum nitride or aluminum oxide, andsimilar materials. Metal-impregnated elastomeric pads may be used at theinterface adjacent the heat sink 74, but not adjacent thewindow/electrode 52 for the same reasons explained above that in generala conductor may not be placed adjacent the window electrode 52. Softmetals such as 1100 series aluminum, indium, copper or nickel may beused at the interface adjacent the heat sink 74, but not adjacent thewindow/electrode 52 for the reasons explained above.

The cooling capability and heating power requirements are best selectedor sized depending on 1) temperature control range required of thewindow/electrode, 2) the minimum and maximum heat internal loads, 3) thematerial properties and physical dimensions of the window/electrode, theheat transfer materials, the heat sink plate and the interfaces betweenheat sink plate, heat transfer materials, and window/electrode, and 4)the temperature of the heat sink. Generally, the cooling capability issized first for the lowest required temperature of operation of thewindow/electrode with the highest internal heat load, and the heatingpower is then sized to overwhelm the cooling for the highest requiredtemperature of operation of the window/electrode with the lowestinternal heat load (typically zero internal heat load).

FIG. 18 corresponds to an enlarged view of a portion of FIG. 5 andillustrates one implementation of the foregoing concept of a thermallyconductive gas interface at both faces (top and bottom) of the thermallyconductive spacer 75 which is not integrally formed with thesemiconductor window electrode 52. In FIG. 18, the overlying cold plate74 sandwiches plural cylindrical spacer rings 75 with the underlyingsemiconductor window electrode 52 as illustrated in FIG. 5. Each spaceror torus 75 can be a material different from the semiconductor windowelectrode 52, as discussed above. A manifold 1000 is formed in the coldplate 74 into which a thermally conductive gas such as helium may besupplied from a source 1010 under positive pressure. Preferably, but notnecessarily, the positive pressure of the source 1010 is selected so asto maintain the pressure within the thin gap between the two partssignificantly above the reactor chamber pressure but below atmosphericpressure. Gas orifices 1020 connect the manifold 1000 to the topinterface 1030 between the cold plate 74 and the spacer 75, permittingthe thermally conductive gas (e.g., Helium) to fill the voids in theinterface 1030. An axial passage 1040 is provided through the spacer 75between its top and bottom faces. The axial passage 1040 connects thetop interface 1030 with a bottom interface 1050 between the bottom faceof the spacer 75 and the underlying semiconductor window electrode 52.The axial passage 1040 permits the thermally conductive gas to flow fromthe top interface 1030 to the bottom interface 1050 to fill voids in thebottom interface 1050, so that the thermally conductive gas fills voidsin both the top and bottom interfaces 1030, 1050. By the source 1010maintaining the thermally conductive gas manifold 1000 under positivepressure (e.g., 5 psi higher than the chamber pressure), the gas flowsto both interfaces 1030, 1050. In order to reduce or prevent leaking ofthe thermally conductive gas from the interfaces 1030, 1050, smallcross-section O-rings 1070, 1080 are sandwiched in the top and bottominterfaces, respectively, at the time of assembly. The O-rings 1070,1080 define nearly infinitesimally thin gas-containing volumes in therespective interfaces 1030, 1050 in communication with the respectivegas manifold 1000, 1040.

FIG. 19 illustrates how the embodiment of FIG. 18 is modified toaccommodate an array of conductive torus spacers 75 integrally formedwith the semiconductor window electrode 52. In this case, the onlyinterface to be filled by the thermally conductive gas is the topinterface 1030.

FIG. 20 corresponds to an enlarged view of a portion of FIG. 5 andillustrates one implementation of the foregoing concept of a thermallyconductive solid interface material at both faces (top and bottom) ofthe thermally conductive spacer 75 which is not integrally formed withthe semiconductor window electrode 52. In FIG. 18, the overlying coldplate 74 sandwiches plural cylindrical spacer rings 75 with theunderlying semiconductor window electrode 52 as illustrated in FIG. 5.Each spacer or torus 75 can be a material different from thesemiconductor window electrode 52, as discussed above. A thermallyconductive solid interface material layer 1085, 1090 is placed in eitheror both the top and bottom interfaces 1030, 1050, respectively. If asolid material layer is placed in only one of the top and bottominterfaces 1030, 1050, then the remaining interface may be filled with athermally conductive gas in the manner of FIG. 18. However, FIG. 20illustrates the case in which a thermally conductive solid interfacematerial layer is in both interfaces 1030, 1050. As discussed above, thesolid interface material layer 1085 in the top interface 1030 may be asoft metal, but the solid interface material layer 1090 in the bottominterface 1050 cannot be highly electrically conductive because it isnext to the electrode 52. The top layer 1085 may be soft aluminum,indium, copper or nickel or an elastomer impregnated with powders orparticles of such metals. Either one of the top and bottom layers 1085,1090 may be an elastomer impregnated with powder or particles of athermally conductive electrically insulating material such as boronnitride, high electrical resistivity (e.g., bulk) silicon carbide orsilicon, aluminum nitride, aluminum oxide and like materials.Alternatively, either one or both of the material layers 1085, 1090 maybe a bonding material, such as thermoplastic, epoxy or an organic orinorganic bonding material.

FIG. 21 illustrates how the embodiment of FIG. 20 is modified toaccommodate an array of conductive torus spacers 75 integrally formedwith the semiconductor window electrode 52. In this case, the onlyinterface to be filled is the top interface 1030.

The invention also solves a severe cooling problem with heated partsinside the reactor chamber which are difficult to cool, such as theheated disposable ring 62 of polymer-hardening precursor materialdescribed above with reference to FIG. 5. (The ring 62 may be heatedonly by plasma heating if no heater is provided, and still requirecooling.) It also solves a problem of heating parts inside the reactorchamber which are difficult to heat directly.

Referring to FIGS. 22 and 23, a cold plate 1100 directly beneath thering 62 and in thermal contact has internal coolant jackets 1110 whichreceive coolant from a coolant circulation pump 1120. The interface 1130between the cold plate 1110 and the ring 62 is filled with a thermalconductivity enhancing substance such as a thermally conductive gas (asin FIG. 22) or a thermally conductive solid material layer 1140 (as inFIG. 23). The thermally conductive gas may be any gas capable ofconducting heat, such as an inert gas or even a gas similar to theprocess gas employed in the reactor chamber, although an inert gas suchas helium is preferred. In the case of the embodiment of FIG. 22employing the thermally conductive gas, a manifold 1150 through the coldplate 1100 is connected to a thermally conductive gas source 1160 whichsupplies thermally conductive gas through the manifold 1160 into theinterface 1130. Leakage of the gas from the interface 1130 is preferablycontrolled to reduce or prevent loss by sandwiching an elastomericlow-cross-section O-ring 1070' between the cold plate 1100 and siliconring 62 at the time the ring is put into its place.

While helium is preferred as the thermally conductive gas in the gap, inthe case of application to heated or cooled parts inside thesub-atmospheric reactor chamber, any gas, including a processing gas,could suffice at a pressure greater than the chamber pressure but belowatmospheric. In such a case, the gas may be allowed to leak into thechamber so that the use of a peripheral seal such as an O-ring orelastomer may not be necessary. Since the thermally conductive gas (or"thermal transfer gas") is pressurized above the chamber pressure, someclamping force must be applied. Such a clamping force can be mechanicalor may be electrostatically induced between the plate 1100 and the ring62. Such an electrostatic clamping feature would require a materialwhich is at least partially electrically insulating to be placed betweenthe plate 1100 and the ring 62. Such a feature can eliminate the needfor a peripheral seal to control leakage of the thermally conductivegas. Such an electrostatic clamping feature is described below in thisspecification with reference to FIG. 26.

The thermally conductive gas can be derived from any suitable source.For example, if the wafer pedestal employs helium cooling underneath thewafer, then a common helium source may be employed for cooling the waferas well as other items (such as the ring 62) inside the chamber.

In the embodiment of FIG. 23, the layer of solid thermally conductivematerial 1140 may be soft aluminum, indium, copper or nickel or anelastomer impregnated with powders or particles of such metals or it maybe an elastomer impregnated with powder or particles of a thermallyconductive electrically insulating material such as boron nitride, highresistivity (e.g., bulk) silicon carbide or silicon, aluminum nitride,aluminum oxide and like materials.

The present invention also concerns cooling chamber walls and chamberliners in a similar manner. Referring to FIG. 24, the chamber side wall50 in any of the reactors discussed above may be cooled by an exteriorcold plate 1210 adjacent a portion of the exterior of the wall 50. Thecold plate includes internal coolant jackets 1220 through which coolantis recirculated by a coolant pump 1230. The interface 1240 between thecold plate 1210 and the side wall 50 is filled with a thermallyconductive gas (such as helium) fed through a manifold 1245 through thecold plate 1210 into the interface 1240 from a gas source 1250 whichmaintains the gas at a positive pressure. Leakage of the thermallyconductive gas from the interface 1240 is reduced or prevented by anO-ring 1260 sandwiched between the cold plate 1210 and the side wall 50at the time of assembly. The O-ring 1260 defines a gas-containing volumeof the interface 1240 which is nearly infinitesimally thin and incommunication with the manifold 1245.

An interior chamber liner 1300 may be cooled by heat conduction to acooled body, such as the side wall 50. In accordance with the presentinvention, such cooling is enhanced by filling the interface 1310between the liner 1300 and the interior surface of the side wall 50 witha thermally conductive gas such as helium. For this purpose, a radialnarrow gas channel 1320 is provided through the side wall 50 to providegas flow between the interface 1240 on the external side wall surfaceand the interface 1310 on the internal side wall surface. The thermallyconductive gas supplied through the manifold 1245 fills the externalsurface interface 1240 and, through the channel 1320, fills the internalsurface interface 1310 between the liner 1300 and the side wall 50. Toprevent or reduce gas leakage, an O-ring 1370 is sandwiched between theside wall 50 and the liner 1300 at the time of assembly. The O-ring 1370defines a nearly infinitesimally thin gas-containing volume within theinterface 1310 in communication with the gas channel 1245 in the sidewall 50.

FIG. 25 illustrates how the embodiment of FIG. 24 is modified bysubstituting a solid material layer 1370, 1380 in each of the interfaces1240 and 1310, respectively, instead of the thermally conductive gas. Inthe embodiment of FIG. 25, each layer 1370, 1380 of solid thermallyconductive material may be soft aluminum, indium, copper or nickel or anelastomer impregnated with powders or particles of such metals or it maybe an elastomer impregnated with powder or particles of a thermallyconductive electrically insulating material such as boron nitride, highresistivity (e.g., bulk) silicon carbide or silicon, aluminum nitride,aluminum oxide and like materials.

FIG. 26 illustrates how the embodiment of FIG. 22 may be modified toinclude the feature of electrostatic clamping of the ring 62 to the coldplate 1100. In FIG. 26, a dielectric layer 1410 is inserted between thepolymer-hardening precursor ring 62 and the cold plate 1100, and anelectrostatic clamping voltage is applied to the cold plate 1100 from aD.C. voltage source 1420 through a clamping switch 1430. Introduction ofthe insulating or dielectric layer 1410 creates a gap 1130a between thecold plate 1100 and the insulating layer 1410 and a gap 1130b betweenthe ring 62 and the insulating layer 1410. The insulating layer 1410 haspassageways 1412 therethrough so that gas supplied from the passageway1150 into the gap 1130a can flow into the other gap 1130b. While FIG. 26shows O-rings 1070' sealing both gaps 1130a and 1130b, such O-rings maynot be necessary, depending upon the electrostatic clamping forceinduced.

The present invention provides a great improvement (by a factor of about6 in the case of the introduction of helium) in thermal conductivityacross the interface between heat-receiving elements of the reactoreither inside the chamber (such as chamber liners, disposable siliconrings) and outside the chamber (such as window electrodes, side walls)and a cooling plate or cold sink. As a result, the automated control oftemperature of many critical parts of the plasma reactor is improved toa new capability exceeding that of the prior art. The inventionaccomplishes this in one or a combination of two characteristic modes atthe various interfaces: (a) the introduction of a thermally conductivegas into the interface and (b) the introduction of a thermallyconductive solid layer in the interface. This, in combination withefficiently controlled heating of the same elements, permits accuratefeedback control of the temperature of each such element thus heated andcooled.

In selecting the heat transfer materials and/or physical dimensions ofthe reactor, the cooling conductance required (G) is determined asfollows:

    G=total maximum internal heat load (watts)/Delta-T1 (degree C.)

where

Delta-T1=Difference between heat sink temperature

and minimum window/electrode temperature.

Alternatively, if the heat transfer materials and physical dimensionshave already been chosen, then the required heat sink temperature may betrivially calculated by rearranging the above equation for Delta-T1 asfunction of G.

Heating power is then determined as follows:

    P=total external heating power required (watts) delivered to control surface,

    P=(G*Delta-T2)--Pmin

where:

G is the cooling conductance from above (in watts/degree C.),

Delta-T2=Difference between heat sink temperature and maximumwindow/electrode temperature

Pmin is the minimum internal heat load on the window/electrode.

EXAMPLE 1

The window/electrode 52 and the heat transfer rings 75 are integrallyformed as a monolithic piece, and the window/electrode 52 is a flatcircular disk 12.81 inches in diameter and 0.85 in thick. Formedintegrally with the window/electrode 52 is an array of four concentriccylindrical heat transfer rings (75) 2" high of the following inside andoutside diameters:

1. outer heat transfer ring--12.80" outside dia., 10.79" inside dia.,

2. middle heat transfer ring--9.010" outside dia., 7.595" inside dia.,

3. inner heat transfer ring--5.715" outside dia., 3.940" inside dia.,

4. center heat transfer ring--2.260" outside dia., 0.940" inside dia.

The window/electrode 52 and integral array of concentric cylindricalheat transfer rings 75 are fabricated together from a single ingot ofpolycrystalline silicon with the following thermal and electricalproperties:

Doping level: 10¹⁴ /cm³, boron or phosphorous

Thermal conductivity: 80 watt/meter*Kelvin

Electrical resistivity: from 20 to 100 ohm*cm

Specific Heat: 0.7 joule/gram*Kelvin

Density: 2.3 gram/cm³

A plurality of 750 watt @ 120 volt rms tungsten filament lamps 76 areemployed. The number of lamps is selected based on measured 73%efficiency (output power/ac input power) and on 400 watt @ 80 volt rmsmaximum operating level (for long lamp life). Two heat zones areemployed, those on the outer circle comprise one zone (outer), and thoseon the inner circle and at the center comprise the second (inner) zone.Each zone has its own temperature measurement (a type-K thermocouplespring loaded against the window/electrode surface) and its own outputtransducer (a phase-angle controller). The lamps, manufactured bySylvania, are deployed as follows:

15 lamps on a 13.55" diameter circle, equal angular spacing (24degrees);

15 lamps on a 6.655" diameter circle, equal angular spacing (24degrees);

1 lamp on central axis.

The outer lamp circle is surrounded on the outside by a cylindricalpolished aluminum reflector that is integral with the heat sink 74.

The outer solenoid antenna 90 is 4 turns comprised of 3/16" diameterwater cooled copper tubing insulated with 1/4" outside diameter teflontubing yielding coil 1" in height and 10" mean diameter, wound asdescribed in the above-referenced parent application.

The inner solenoid antenna 42 is 4 turns comprised of 3/16" diameterwater cooled copper tubing insulated with 1/4" outside diameter teflontubing yielding coil 1" in height and 3.25 mean diameter, wound asdescribed in the above-referenced parent application.

The heat sink plate 74 is a water cooled aluminum plate maintained at 75degree C. by a closed loop heat exchanger using a 50/50%water/ethylene-glycol mixture at a flow rate of 2 gallons per minute.The heat sink 74 houses lamp sockets and provides cooling for the lamps76 required due to inherent lamp losses to socket (approximately 27%).The heat sink plate 74 includes feed-through for the inner and outersolenoidal antennas 42, 90. The heat sink 74 also functions as a groundplane for the antennas 42, 90. The heat sink plate 74 includes O-ringgrooves to accommodate 0.139 inch diameter, 30 durometer soft O-ringsdeployed just inside the outer diameter of each heat transfer ring 75and just outside the inner diameter of each heat transfer ring 75. Theheat sink 74 is mounted on top of the integral array of concentriccylindrical heat transfer rings 75. Surface roughness of both surfaces(the bottom of the heat sink 74 and the top of heat transfer rings 75)is less than a micro-inch. Flatness of each surfaces is less than 0.0005inch. The effective gap between the bottom of the heat sink and the topof the heat transfer rings is less than 0.001 inch.

EXAMPLE 2

The window/electrode 52 and the heat transfer rings 75 are separatepieces formed of different materials. The window/electrode 52 is a flatcircular disk 14.52 inches in diameter and 0.85 inches thick. A separatearray of 4 concentric cylindrical heat transfer rings 75 2" high of thefollowing inside and outside diameters is placed in between the heatsink plate and the window electrode:

1. outer heat transfer ring--12.701" outside dia., 10.67" inside dia.,

2. middle heat transfer ring--8.883" outside dia., 7.676" inside dia.,

3. inner heat transfer ring--5.576" outside dia., 3.920" inside dia.,

4. center heat transfer ring--2.080" outside dia., 1.050" inside dia.

The window/electrode 52 is fabricated from a single ingot ofpolycrystalline silicon with the following thermal and electricalproperties:

Doping level: 10¹⁴ /cm³, boron or phosphorous

Thermal conductivity: 80 watt/meter*Kelvin

Electrical resistivity: 20-100 ohm*cm

Specific Heat: 0.7 joule/gram*Kelvin

Density: 2.3 gram/cm³

The array of concentric cylindrical heat transfer rings 75 arefabricated from SiC (silicon carbide) with the following thermal andelectrical properties:

Thermal conductivity: 130 watt/meter*Kelvin

Electrical resistivity: 10⁵ ohm*cm

Specific Heat: 0.655 joule/gram*Kelvin

Density: 3.2 gram/cm³

A plurality of 750 watt @ 120 volt rms tungsten filament lamps areemployed. The number of lamps is selected based on measured 73%efficiency (output power/ac input power) and 400 watt @ 80 volt rmsmaximum operating level (for long lamp life). Two heat zones areemployed, those on the outer circle comprise one zone (outer), and thoseon the inner circle and at the center comprise the second (inner) zone.Each zone has its own temperature measurement (a type-K thermocouplespring loaded against the window/electrode surface) and its own outputtransducer (a phase-angle controller). The lamps 76, manufactured bySylvania, are deployed as follows:

15 lamps on 13.55" diameter circle, equal angular spacing (24 degree);

15 lamps on 6.626" diameter circle, equal angular spacing (24 degree);

1 lamp on central axis.

The outer lamp circle is surrounded on the outside by a cylindricalpolished aluminum reflector that is integral with the heat sink.

The outer solenoid antenna 90 is four turns comprised of 3/16" diameterwater cooled copper tubing insulated with 1/4" outside diameter teflontubing yielding coil 1" in height and 10" mean diameter, wound asdescribed in the above-referenced parent application.

The inner solenoid antenna 42 is four turns comprised of 3/16" diameterwater cooled copper tubing insulated with 1/4" outside diameter teflontubing yielding coil 1" in height and 3.25 mean diameter, wound asdescribed in the above-reference parent application.

The heat sink plate 74 is a water cooled aluminum plate maintained at 75degrees C. by a closed loop heat exchanger using a 50/50%water/ethylene-glycol mixture at a flow rate of 2 gallons per minute.Heat sink houses lamp sockets and provides cooling for the lamps,required due to inherent lamp losses to socket (approximately 27%). Theheat sink plate 74 includes feed-through for the aforementioned innerand outer solenoidal antennas 42, 90. The heat sink 74 also functions asa ground plane for the antennas. The heat sink plate 74 and thewindow/electrode 52 include O-ring grooves to accommodate 0.139 inchdiameter, 30 durometer soft O-rings deployed just inside the outerdiameter of each heat transfer ring 75 and just outside the innerdiameter of each heat transfer ring 75. The heat sink 74 is mounted ontop of the array of concentric cylindrical heat transfer rings 75.Surface roughness of all surfaces (bottom of the heat sink and top ofthe heat transfer rings, bottom of the heat transfer rings and top ofthe window/electrode) is less than a micro-inch. Flatness of eachsurface is less than 0.0005 inch. The effective gap between the bottomof the heat sink and the top of the heat transfer rings is less than0.001 inch. The effective gap between the bottom of the heat transferrings and the top of the window/electrode is less than 0.001 inch.

While the invention has been described in detail by specific referenceto preferred embodiments, it is understood that variations andmodifications thereof may be made without departing from the true spiritand scope of the invention.

What is claimed is:
 1. A plasma reactor comprising:a plasma reactorchamber and a workpiece support for holding a workpiece adjacent asupport plane inside said chamber during processing, said chamber havinga reactor enclosure portion facing said support; a cold sink adjacentsaid reactor enclosure portion; a plasma source power applicator betweensaid reactor enclosure portion and said cold sink; and a thermalconductor between and in contact with said cold sink and said reactorenclosure; wherein said palsma source power applicator comprises pluralradially dispersed applicator elements defining voids therebetween andsaid thermal conductor comprises radially dispersed thermally conductiveelements in said voids and contacting said cold sink and said reactorenclosure portion.
 2. The reactor of claim 1 wherein said radiallydispersed thermally conductive elements comprise respective concentriccylindrical rings.
 3. The reactor of claim 1 wherein said reactorenclosure portion comprises a ceiling, said ceiling comprising a windowfor power emanating from said plasma source power applicator.
 4. Thereactor of claim 3 wherein:said plasma source power applicator comprisesan inductive antenna comprising plural inductive elements, saidinductive antenna being in communication with an RF power generator; andsaid ceiling comprises an inductive power window.
 5. The reactor ofclaim 4 wherein said ceiling comprises a semiconductor window electrode.6. The reactor of claim 1 wherein said thermal conductor and said coldsink define a cold sink interface therebetween, said plasma reactorfurther comprising:a thermally conductive substance within said coldsink interface for reducing the thermal resistance across said cold sinkinterface.
 7. The reactor of claim 6 wherein said thermal conductor isformed separately from said reactor enclosure portion whereby a reactorenclosure interface is defined between said reactor enclosure portionand said thermal conductor, said plasma reactor further comprising:athermally conductive substance within said reactor enclosure interfacefor reducing the thermal resistance across said reactor enclosureinterface.
 8. The reactor of claim 7 wherein said thermally conductivesubstance in said reactor enclosure interface comprises a thermallyconductive gas filling said reactor enclosure interface.
 9. The reactorof claim 7 wherein said thermally conductive substance in said reactorenclosure interface comprises a thermally conductive solid material. 10.The reactor of claim 9 wherein said thermally conductive solid materialin said reactor enclosure interface comprises an elastomer impregnatedwith particles of a thermally conductive material.
 11. The reactor ofclaim 6 wherein said thermally conductive substance comprises athermally conductive gas filling said cold sink interface.
 12. Thereactor of claim 11 further comprising:a gas manifold in said cold sinkcommunicable with a source of said thermally conductive gas; an inletthrough said cold sink from said gas manifold and opening out to saidcold sink interface.
 13. The reactor of claim 12 further comprising anO-ring apparatus sandwiched between said cold sink and said thermalconductor and defining a gas-containing volume in said cold sinkinterface in communication with said inlet from said cold sink.
 14. Thereactor of claim 6 wherein said thermally conductive substance comprisesa thermally conductive solid material.
 15. The reactor of claim 14wherein said thermally conductive solid material comprises a soft metalof the type comprising one of aluminum, indium, copper, nickel.
 16. Thereactor of claim 14 wherein said thermally conductive solid materialcomprises an elastomer impregnated with particles of a thermallyconductive material.
 17. The reactor of claim 16 wherein said particlesof a thermally conductive material are electrically resistive andthermally conductive.
 18. The reactor of claim 17 wherein said particlescomprise one of boron nitride, resistive silicon carbide, resistivesilicon, aluminum nitride, aluminum oxide.
 19. The reactor of claim 16wherein said particles comprise a metal.
 20. The reactor of claim 6wherein said thermal conductor is integrally formed with said reactorenclosure portion.